The invention relates generally to a method for forming a horn reflector antenna; and more particularly, relates to a mold for forming conical horn antennas.
A conical horn reflector antenna is generally formed by the right angled intersection of a cone with a cylinder, although other angular relationships may be suitable. The intersection defines the perimeter of an offset paraboloid section with respect to the X and Y orthogonal axis. The parabolic focal length for a right-angled horn reflector is one half the length of the axis of the cone between the apex and the intersection with the offset paraboloid. Thus, the conical horn reflector antenna includes three geometric shapes; a conical horn, a parabolic section and a cylindrical section. Spherical radio-frequency (RF) waves from the conical horn diverge on the parabolic reflector, and are transformed into planar wave fronts, which radiate from the circular projectile aperture at the outer end of the cylindrical section.
The RF performance of the conical horn antenna is critically dependent upon the accuracy in forming the parabolic reflecting surface and the maintenance of the feed source and the exact focal point of the parabolic surface. Performance is also dependent upon the mechanical and electrical contact at the intersecting joints between the various sections of the antenna. Any gaps at such intersections may result in appreciable RF leakage, which may significantly affect the radiation pattern and render the antenna virtually uselsss. Usually, the antenna is filled with dried pressurized gases and an air tight membraneous window having no effect on the passage of electromagnetic energy is used to enclose the projectile circular aperture of the antenna. If the dried gases within the antenna are dissipated via any air gaps, moist air may enter the antenna and condense into water. An appreciable accumulation of water will substantially degrade performance, and may even cause the antenna to become inoperative.
Generally, the horn reflector antennae are formed by sheet metal fabrication or fiberglas molding. Sheet metal fabrication requires independent formation of each geometric shape with a plurality of metal pieces.
In sheet metal fabrication, optimum tolerances of the various parts, individually and after assembly, are difficult to maintain, and, frequently varied so appreciably from the optimu, to cause measurable degradation in the antenna performance. Often, the economics made optimum design tolerances unfeasible. Furthermore, the multiplicity of joints between parts compounded the probability of RF and air leakage problems.
In prior fiberglas constructions, usually the cone part of the antenna was fabricated from one tool and a combined paraboloid and cylindrical part from another tool. In some instances, when optimum performance was not required, only the cone and paraboloid parts were independently formed, and the cylindrical portion was omitted. However, the elimination of the cylindrical portion degrades antenna performance by removing an important shielding element. Although prior fiberglas techniques enabled antenna constructions to be made in multiple sections, significant errors were made in the relationship of the component antenna sections during assembly. Furthermore the joint(s) at the interface of the attached sections was still a source of significant RF and gas leakage.
An example of a multiple section fiberglas antenna construction may be found in U.S. Pat. No. 3,510,873 (Trevisan-1970). In an embodiment disclosed therein, the antenna included a cone unit and paraboloid-cylindrical unit connected together at a flanged joint. These assembled units were then connected to a feed or receive wave guide arrangement by a "union" or "transitional" element. The union element was bolted at one end to the cone at the other end to the wave guide. To achieve optimum performance, the focal point of the parabolic reflector must be coincident with the central axis of the wave guide. An error or deviation of the union element from the optimum position, in either the axisl or radial direction, will have substantial, if not the greatest single effect on the electrical performance of the antenna. Thus, the Trevisan antenna, although referred to as a two unit construction is actually a three part construction consisting of the paraboloid-cylindrical unit, the cone unit, and the union element unit.
The aforesaid Trevisan patent also refers to a single unit antenna construction. The union element, which is so essential for antenna performance was not considered as an antenna element. Thus, this antenna is actually a two unit antenna to wit: the paraboloid-cylindrical and cone unit and the union element unit. The subject invention, on the other hand, provides a single-piece antenna having the union element as an integral part thereof, without requiring mechanical connection between the horn and such union element.
As aforestated, the Trevisan Patent refers to a single piece horn-reflector antenna (which does not include the union element), but it is noted that the Trevisan patent does not disclose the means or tooling for fabricating the single-piece antennae. The invention herein discloses a method for forming a single piece antenna including a union element, and such method enables repeatible fabrication of such single piece antenna.
In prior fiberglas methods, flexible tools or molds were frequently used for forming one or more of the various units of the antenna. Thus, to subsequently remove the tool, it was necessry to distort or bend the tool during its removal from the fiberglas section. Such distortion at times became permanent, and any sections subsequently formed from the same tool, were dimensionally imperfect. Flexible tooling is generally undesirable, since it introduces another source for developing dimensional error. The subject invention overcomes this problem by disclosing a method for forming a single-piece horn-reflector antenna, by the use of rigid dimensionally stable tooling, which may be repeatedly reused without effecting mechanical or electrical antenna specifications. The main mold parts are removable from the radiating aperture of the antenna.
It is therefore a primary object of this invention to provide a method for forming a single piece horn antenna.
Another object is to provide a method to enable accurate and repeatible spatial relationship to be maintained between the horn and the other geometric sections of the horn-reflector antenna.
Another object is to provide a method which enables strict tolerances of antenna dimensions to be maintained and easily repeated in subsequent antenna fabrications; and thereby providing substantially identical performance between antennas.
Another object is to provide a simplified method for forming high frequency antennas after it is fabricated.
Another object is to provide a method for forming horn-reflector antennas utilizing one section for forming a paraboloid-cylinder portion of the antenna and two sections for forming the horn portion of the antenna.
Another object is to provide a method for fabricating antennas utilizing substantial portions of the same tooling to form various antenna configurations in a single piece.
Still another object is to provide a method for forming horn type antennas which enables "transitional" portion to be formed to the horn portion of the antenna, whereby optimum coupling of the electromagnetic waves is achieved between the horn and the associated wave guide of the transmitter or receiver system.